The present invention relates to an improvement of a wheel for rolling stock having such a form that a rim section is deflected from a boss section towards the outside of a track and relates to a manufacturing method thereof.
A wheel for rolling stock (hereinafter, referred to as a wheel) requires a performance against a cracking damage due to a thermal crack occurring on a tread or flange surface of the wheel, namely, requires durability against cracking damage, because of a thermal stress due to mainly brake heat under such a circumstance that the brake heat is raised in response to recent increase in high-speed travel via railroad.
As a conventional technique which satisfies the above requirement, there exist a method of decreasing heat sensitivity of a material or improving fracture toughness, and a method of decreasing a thermal stress generated by braking, etc. due to improvement in a form of a wheel. As a technique which belongs to the latter method, the applicant of the present invention has suggested a wheel for rolling stock in Japanese Patent Application Laid-Open No. 56-34504 (1981).
FIG. 1 is an explanatory drawing showing a deflection amount .delta. and deflection angle .theta. of a rim section 1 relative to a boss section 3 in a solid rolled wheel for rolling stock (hereinafter, referred to as a solid rolled wheel). In the wheel disclosed in Japanese Patent Application Laid-Open No. 56-34504 (1981), as shown in FIG. 1, an end of a curved line of the side of a fillet closer to a flange 2 of the rim section 1 of the wheel is a point A1, a position on the side opposed to the flange where a plate thickness of a wheel disk wheel disk section 4 is minimum relative to the point A1 is a point A2, and a mid-point between the points A1 and A2 is a point A3. Similarly, an end of a curved line on a side opposed to the flange of the fillet of the boss section 3 is a point B1, a position on the side closer to the flange where the plate thickness is minimum relative to the point B1 is point B2, and a mid-point between the points B1 and B2 is a point B3. Lines from the points A3 and B3, which are perpendicular to a center line O of the wheel, are represented by La and Lb respectively, and a dimension between the lines La and Lb, namely, a deflection amount of the rim section 1 is represented by .delta., and an angle between a line linking the points A3 and B3 and the line La or Lb, namely, a deflection angle of the wheel disk section 4 is represented by .theta.. At this time, in the case where any wheel whose diameter is equivalent to the above one is used, there is a tendency that as the deflection amount .delta. is larger, the thermal stress which is generated in the wheel disk section 4 of the wheel is smaller.
Needless to say, when the deflection amount .delta. changes, the deflection angle .theta. also changes simultaneously. For this reason, the similar change is shown as to action of the thermal stress of the wheel disk section 4 with respect to the deflection angle .theta.. A relationship between the deflection amount .delta. and the maximum value of the thermal stress in the wheel disk section 4 is shown in FIG. 2. According to this result, when the deflection amount .delta..gtoreq.40 mm, the thermal stress generated at the time of braking can be lowered remarkably, and a wheel having excellent brake-resistance performance can be obtained. Here, since the relationship between the deflection angle .theta. and the maximum value of the thermal stress of the wheel disk section 4 is approximately the same as the relationship between the deflection amount .delta. and the maximum value of the thermal stress of the wheel disk section 4, the description thereof is omitted.
As mentioned above, the solid rolled wheel of conventional wheels has limitation in the manufacturing technique that the point A3 in FIG. 1 is positioned approximately in the center of an axial direction, parallel to the center line 0, of an inner diameter of the rim section 1. FIG. 3 is an explanatory drawing showing a deflection amount .lambda. of the wheel disk section in the solid rolled wheel. As shown in FIG. 3, when a line, which is perpendicular to the center line 0 of the wheel and passes through the point A3 which is the mid-point between the points A1 and A2, is represented by La, and a mid-point in the axial direction of the inner diameter of the rim section 1 is represented by a point C, and a line, which is perpendicular to the center line 0 of the wheel and passes through the point C is represented by Lc, a distance between the lines La and Lc, namely, the deflection amount .lambda. is approximately zero. As a result, even if the deflection amount .lambda. is made larger in the design, the deflection amount .lambda. according to the design cannot be obtained, and only a value of zero or close to zero is obtained in the most cases.
Therefore, in the case of the rolled wheel, it is necessary to satisfy the condition that the deflection amount .delta..gtoreq.40 mm with only by the deflection amount of the point B3 in the center of the plate thickness adjacent to the end of the curved line on the side opposed to the flange of the fillet of the boss section 3. For this reason, it is difficult to obtain the condition that the deflection amount .delta..gtoreq.40 mm in a wheel for locomotive, etc. having a hub cut and a larger diameter. Moreover, since the deflection amount .lambda. is approximately zero, the maximum value of the deflection amount .delta. is not so larger, and thus the deflection angle .theta. of the wheel disk section 4 shown in FIG. 1 cannot obtain a larger value. As a result, since the occurrence of the thermal stress cannot be sufficiently suppressed, there arose a problem that the durability against a cracking damage cannot be improved more than some degree.